Spoilt for choice - Intercomparison of four different urban climate models

Abstract

In recent years, different models to simulate urban climate variables have been applied to various cities. As the model outputs are usually validated individually, this raises the question about which urban climate model to choose for what specific purpose. The present study aims to find answers to this by intercomparing air temperature outputs of four different urban climate models that have been applied in the city of Bern, Switzerland. This includes a geostatistical land use regression model and the numerical models MUKLIMO_3, PALM, and FITNAH 3D. Using data from 70 stations of an urban air temperature measurement network, we intercompare the four models by focusing on the modeled urban air temperature variability. MUKLIMO_3 outputs show a weak urban air temperature variability, while strong small-scale temperature gradients are modeled by FITNAH 3D. PALM outputs are the only ones that reproduce the impact of a large-scale ventilation pattern, but have a large positive bias. The most accurate estimates of the urban air temperature variability are obtained from the land use regression model. For future applications of urban climate models, we reinforce the need of validation with in-situ measurements, since the outputs (and subsequent policies) depend substantially on the selection of the model.